VS_Filt()            Interactively build a filter

Description:

  VS_Filt() provides a non-screen destructive user interface to allow
  the user to select a list of fields, logical connectives and
  comparison constants from pop-up lightbar windows.

Syntax:     

  c_Filter = VS_Filt()

Pass:       

  Nothing

Return:     

  c_Filter is a character expresstion that will contain the desired
  filter (blank if the user specified "no filter").

Notes:      


Example:    

  c_Filter = VS_FILT()
  IF EMPTY(c_Filter)
     c_Filter = ".T."
  ENDIF
  DO WHILE &c_Filter
     .
     .
     .
     SKIP
  ENDDO

Usage:      

  VS_Filt() is designed to provide the uninitiated user with an easy
  interface to "filter" specification building.  It is database
  independent and limits the choices available in the light bar menus to
  those that are applicable to the variable type selected.  As the user
  selects fields, relational operators and comparison constants, the
  string VS_Filt() builds is also displayed on the screen.

  VS_Filt() alone is not a powerful function, but when combined with the
  macro substitution capabilities of Clipper, the two become very
  powerful indeed.  The string returned by VS_Filt() is suitable for
  macro subsitution in the SET FILTER TO command as well as any FOR
  clause in any Clipper command supporting that clause (such as REPORT,
  SORT, COPY, LIST, DO WHILE, etc.)